Metalworking lubricant solution



Patented Mar. 17, 1953 HTED STATES ATET OFFICE No Drawing. Application May 13, 1949, Serial No. 93,187

15 Claims. 1

This invention relates to wire drawing lubricants and more particularly to water-soluble wire drawing lubricants.

In the drawing of wire, particularly small diameter wire, it is customary to pass the wire through the drawing die while immersed in an aqueous cooling and lubricating solution. Many different combinations of materials in solution, suspension, or in colloidal dispersion in water, have heretofore been proposed as lubricants in such aqueous cooling solution. The most effective lubricant in aqueous solution in such wire drawing practice is an alkali metal fatty acid soap compound. However, it has been found that such soap compounds are subject to decomposition by reaction with water-hardening constituents and heavy metal ions present in the solution with formation of insoluble fatty acid soap compounds. Moreover, it has been found that the alkaline pH of the soap solution causes the precipitation of many metal ions as insoluble hydrated oxide compounds which generally interfere with the drawing of the metal wire through the die. Further, it is found that the surface of many metal wires are detrimentally corroded by the alkaline pH wire drawing alkali metal fatty acid soap solution.

The object of this invention is to overcome these several disadvantages of such alkali metal fatty acid soap solutions, thereby to improve the utility of the same as wire drawing solutions.

Another object is to increase the lubricating properties of such soap solutions.

Still another object is to stabilize the lubrieating and coolant properties of such soap solutions.

Other objects will be apparent as the invention is more fully hereinafter disclosed.

In accordance with these objects I have discovered that the bi-metallic salts of ethylene diamine tetra-acetic acid are, per se, excellent lubricants in aqueous solution and that when they are used in combination with alkali metal fatty acid soap compounds, soap solutions of superior lubricating properties are obtained, said solutions being free of the objections and disadvantages heretofore experienced.

By the term bi-metallic salts of ethylene diamine tetra-acetic acid I mean to identify those salts in which at least two of the carboxylic groups of the acid but not over three such groups are neutralized by an alkali metal ion and the remaining carboxylic groups are neutralized by a metal ion other than an alkali metal ion. By

alkali metal ion 1 mean to identify an ion of '.the

group consisting of Li, K, Na and Cs. Of these compounds the sodium and potassium salts are the most readily available and the most compatible with sodium and potassium salts of the fatty acids in aqueous solutions.

These bi-metallic salts of ethylene diamine tetra-acetic acid are of two general types, i. e., those in which the second metal ion is above the metal being drawn in the displacement series of metals in aqueous solutions of the bi-metallic salt and those in which the second metal ion is below the metal being drawn in the said displacement series. Either of these two types are utilizable in the present invention but the. mechanism by which they accomplish the improved result differs.

The invention will be described as it has been adapted for use in the drawing of the base metals Fe, Ni and Cu and their alloys with these two types of salts when used in association with the sodium salts of the fatty acids. In this adaptation the di-sodium, bi-metallic salt of ethylene diamine tetra-acetic acid is preferred because of its better compatibility with the sodium salts of the fatty acids.

In the drawing of iron and steel alloys into small diameter wire While using a coolant and lubricating solution consisting of an aqueous solution of a sodium salt of a fatty acid, such as sodium stearate, the soap solution gradually accumulates a deposit of hydrated metal oxides and insoluble soap compounds which materially interfere with drawing the wire and often causes undue wear on the die opening. The addition of the usual type of deionizing agents to the aqueous soap solution only partially overcomes this accumulation by inhibiting the precipitation of some of the insoluble soap compounds. The tetra-sodium salt of ethylene diamine tetraacetic acid is about the best deionizing agent to add to such a soap solution for this purpose, as this salt by the formation of complexes with lesser basic metal ions present in solution, inhibits substantially completely the formation of such insoluble soap compounds and to a marked degree also inhibits the precipitation of many hydrated metal oxide compounds.

However, the alkaline pI-I solution thus produced is strongly corrosive towards iron and iron alloys forming hydrated iron oxide on the surface thereof which are abrasive towards the die surface as the wire passes through the die.

I have discovered that the addition of a substantial amount of a bi-metallic salt of ethylene diamine tetra-acetic acid, of either of the two NaOOC-HzC CHnCOONa This salt is best formed by dissolving one molar weight of the tetra amino acid in an aqueous solution containing two molar weights of NaOl-l and digesting this solution at a warm to hot temperature with one molar weight of freshly precipitated calcium hydroxide until the hydroxide is completely dissolved; To recover this salt from the resulting solution the solution is evaporated to dryness. The salt is a white, amorphous solid, stable in air and highly soluble in water. In aqueous solution it is a strong complexing agent towards most metal ions forming highly soluble and stable complexes therewith that are exceedingly di'fiicult to break down chemically. In the presence of alkali metal fatty acid soap compounds in aqueous solutions, the fatty acid appears to be the stronger acid and. inter-action with formation of insoluble calcium soap compounds does not occur.

In association with fatty acid soap compounds in aqueous solution, the Na-Ca bi-metallic salt appears to function as an anti-oxidant towards the metal surface of the drawn wire inhibiting the formation thereon of surface metal oxides thereby reducing die wear.

The amount of this salt permissible in such soap solutions may be varied widely without es.- sential departure from the invention from a small amount to a large amount. Aqueous solutions of this salt are excellent drawing solutions, per se, but do not have quite enough body. The addition of a small amount of a fatty acid soap compound to the solution will. increase the body of the solution materially. Conversely, the addition of a small amount of the bi-metallic salt to a soap solution thins the solution somewhat but increases its lubricating. properties as well as lowering its corrosion properties. The best results appear to be obtained'with a. drawing. solution that contains about equal amounts, by weight,v of a soap compound and a bi-metallic salt at a dilution giving the desired body to the lubricating solution, which varies with respect to the size wire being drawn, the speed. of draw, and the percent reduction in area per draw. Generally speaking, with increase in' speed of draw the density of the drawing lubricant is increased, the percent reduction in. area remai i a constant. However, as the wire sizedecreases it is generally desirable to decrease the density of the lubricating solution materially. This increase and decrease in density is usuall accomplished by varying the amount of water present in the drawing solution. In the forming of the present drawing solution, water deionized preferably with the tetra sodium salt of ethylene diamine tetra-acet c acid is employed.

As typical examples of such wire drawing solutions the following may be given:

Example #1 For medium diameter wire, a solution containing equal amounts, by weight, of sodium stearate and the di-sodium, mono-calcium salt of ethylene diamine tetra-acetic acid having a density of about 1.1.

Example #2 For small diameter wire, a solution containing equal amounts, by weight, of sodium stearate and the (ii-sodium, mono-calcium salt of ethylene diamine tetra-acetic acid having a density of about 1.0..

Example #3 For fine diameter wire, a solution containing equal amounts, by weight, of sodium stearate and the (ii-sodium, mono-calcium salt of ethylene diamine tetra-acetic acid having a density of about 0.98.

In these examples, the relative proportions of soap to salt may be varied widely without essential departure from the invention as may also the density of the solutions, as hereinabove explained, to meet varying drawing conditions.

In substitution for the sodium stearate, any other water soluble; alkali metal salt of a fatty acid and. mixtures of two or more of said soap compounds may be employed. In substitution for the di-sodiumemono-calcium salt of the amino acid. any (ii-sodium. mono-alkaline earth metal salt may be employed as may also any dialkali metal-mono-alkaline earth metal salt may be employed. However,, it is preferable to employ the same alkali metal in. both compounds to obtain compatibility, although the sodium and potassium salts appear to mix, well in aqueous solutions being closely similar in their relative basicities.

By the use of these lubricating solutions greater drawing speeds, longer die life and longer time intervals for effective lubricating solution life, are obtained thereby facilitating the wire drawing operation materially.

The above solutions are utilizable with all base metals and their alloys the bi-metallic salt being stable in aqueous solution, against decom- Position by metal displacement reaction with said base metals, the calcium being higher than the base metals in the displacement series.

The second type of bi-metallic salt utilizable in the present. invention is one in which at least two but not more. than. three carboxylic groups of the tetra acid are neutralized by an alkali metal ion, preferably sodium. and the remaining carboxylic groups are neutralized by a metal ion displaceable. by the base metal of the, wire being drawn. In this type of salt the second metal is preferably one of known. lubricating properties, such as lead, cadmium and copper.

This type of salt is readily formed in the same manner above described by the (ii-sodium, monocalcium salt, and mayv berecovered from aqueous solution similarly.

Aqueous solutionsofthis typeof biemetallic salt are excellent drawing lubricants, per se, the second metal being deposited upon the surface of the wire in a mom-atomic film layer as the fresh surface of the wire is exposed in passing through the drawing die. thereby lubricating the wire surface and protecting the die face from abrasion.

In association with this type of bi-metallic salt. alkali metallfatty acid soap compounds improve the lubricating properties of the solution but conversely to the other type of lubricating solution the bi-metallic salts of this type must always be used in large excess of the soap compounds, inasmuch as they are constantly being used up during the drawing operation and displaced by bi-metallic salts of the base metal of the wire which while being somewhat lubricating, per se, and having strong complex forming properties, nevertheless do not function as lubricants to the same efficiency and in the same manner as the original bi-metallic salts.

As one specific example of this type of lubricant solution, the adaptation of the same to the drawing of beryllium-copper alloys will be described. In this type of alloy, the solid solution phase gradually decomposes on cold working, as by cold drawing, with precipitation of a finely dispersed hard phase which rapidly wears away the die surface. Heretofore in the art, it has been proposed to surface the wire before drawing with cadmium to protect the die surface from such abrasion wear. The difficulty is that the cadmium deposited on the surface prior to drawing does not evenly disperse itself over the wire surface during drawing with the result that the wire diameter varies.

In accordance with the present invention by the use of a drawing lubricant solution that contains the di-sodium, mono-cadmium salt of ethylene diamine tetra-acetic acid the surface of the beryllium-copper wire is coated with a monatomic film layer of metallic cadmium by displacement reaction with the copper of the beryllium-copper alloy as fast as any fresh surface of the copper alloy is exposed to the solution during drawing, the depth of the cadmium coating remaining constant at a noon-atomic film layer as the diameter of the wire decreases, thereby eliminating variations in wire diameter incident to such variations in cadmium thickness. Moreover, such a mom-atomic cadmium layer is tenacious in adhering to the surface of the copper alloy and is not subject to stripping therefrom in passing through the die.

As a typical example of this type of drawing lubricant solution, I prefer to employ a solution of the di-sodium, mono-cadmium salt of ethylene diamine tetra-acetic acid of the proper density for the particular wire drawing operation in view, substantially as above described, which contains from 1% to 20% alkali metal fatty acid soap compounds, preferably sodium stearate. In making up this solution the water employed is first deionized, preferably with the tetra sodium salt of ethylene diamine tetra-acetic acid, in excess of that amount normally required, the amount of said excess not being materially important but should at least be substantial. In this deionized water the desired proportion of the di-sodium, mono-cadmium salt is dissolved and sodium stearate in an amount from 1% to 20% of this weight of salt is then added to the solution. As a typical example of such a drawing solution, 25 grams of the bi-metallic salt and 2.5 grams of sodium stearate in 1000" cc. H2O deionized with 2 to 5 grams ethylene diamine tetra-acetic acid tetra-sodium salt provides an excellent drawing solution for beryllium-copper alloys of the 2% Be type.

This drawing solution has one major advantage in that it can be employed as a warm to hot drawing solution, if desired, to facilitate the displacement reaction providing the lubricating film of cadmium on the wire surface.

The bi-metallic copper salt may be employed in the drawing of many iron-base alloys which evidence similar difficulties on drawing.

The bi-metallic lead (Pb) salt also may be employed in the drawing of other types of alloys to provide a lubricating film of lead on the surface of the alloy.

The drawing solution may be repeatedly fortified with the bi-metallic salt to extend or prolong the operating life of the drawing solution, the accumulation of the displacement bi-metallic salts in the solution not being detrimental as such bi-metallic salts and complexes of this amino acid have an extremely high solubility in the aqueous solution and are lubricants, per se, in aqueous solution.

Whereas the above invention has been described specifically as it has been adapted for use with the bi-metallic salts of ethylene diamine tetra-acetic acid, the poly-metallic salts of polyamino-polycarboxylic acids generally react similarly, particularly those polyamino-polycarboxylic amino salts that are known and recognized as chemical equivalents for ethylene diamine tetra-acetic acid, such as the ethylene and acetic acid homologues of ethylene diamine tetra-acetic acid and by the term ethylene diamine tetra-acetic acid as it hereinafter appears in the claim is meant such polyaminopolycarboxylic acids as are substantial chemical equivalents for this acid for the purposes of this invention.

Having described the above invention generically and specifically and given several specific embodiments thereof, it is believed apparent that the same may be widely varied without essential departure therefrom and all such modifications and departures are contemplated as may fall within the scope of the following claims.

What I claim is:

1. A cooling-lubricant solution consisting of an aqueous solution of a "bi-metallic salt of ethylene diamine tetra-acetic acid, said salt having at least two and not more than three of its four carboxylic groups neutralized by an alkali metal ion and the remaining carboxylic groups neutralized by a metal ion other than an alkali metal ion.

2. A cooling-lubricant solution consisting of an aqueous solution of a bi-metallic salt of ethylene diamine tetra-acetic acid, said salt having two of its four carboxylic groups neutralized by sodium ions and the remaining carboxylic groups neutralized by a di-valent metal ion.

3. A cooling-lubricant solution consisting of an aqueous solution of a bi-metallic salt of ethylene diamine tetra-acetic acid, said salt having two of its four carboxylic groups neutralized by sodium ions and the remaining carboxylic groups neutralized by an alkaline earth metal ion.

4. A cooling-lubricant solution consisting of an aqueous solution of a bi-metallic salt of ethylene diamine tetra-acetic acid, said salt having two of its four carboxylic groups neutralized by sodium ions and the remaining carboxylic groups neutralized by a calcium ion.

5. A cooling-lubricant solution consisting of an aqueous solution of a bi-metallic salt of ethylene diamine tetra-acetic acid, said salt having two of its four carboxylic groups neutralized by sodium ions and the remaining carboxylic groups neutralized by a cadmium ion.

6. A cooling-lubricant solution consisting of an aqueous solution of a "bi-metallic salt of '7 ethy ene diamine tetra-acetic acid, said salt having two of its four .carboxylic groups neutralized by sodium ions and the remaining carhoxylic groups neutralized :by a copper ion.

Z. In the cold drawing .of base metal Wires. the improvement which comprises drawing the same while immersed in an aqueous solution c taining a di-alkali "metal bi-metallic salt of ethylene diamine tetra-acetic acid.

.8. In the cold drawing of copper alloys, the improvement which comprises drawing the same While immersed in an aqueous solution containing the di-sodium, mono-cadmium salt or" ethylene diamine tetra-acetic acid.

'9. In the cold drawing of ferrous alloys, the improvement which comprises drawing the same while immersed in .an aqueous solution containing the -di-sodium, mono-calcium salt of ethylone diamine tetra-acetic acid.

1.0. A Wire drawing lubricant solution for base metals and their alloys, said solution containing about equal amounts byweight of an alkali metal fatty acid soap and a .di-alkali metal .mono alkaline earth metal salt of ethylene diamine tra acetic acid dissolved in deionized water sufiieient in amount to provide a density to the solution of from 9.98 to ,1.1.

11. The Wire drawing solution of claim 10, s id alkali metal fatty acid soap consisting of sodium ste rate.

1,2. The Wire drawing solution of claim 10, said di-alkali metal mono alkaline earth metal salt consisting of the fil-SOdilllll mono calcium salt of ethylene diamine tetra acetic acid.

13. The wire drawing solution of claim 10, de-ionized water consisting of water containing a proportion of the tetra sodium salt of ethylene diamine tetra acetic acid sufiicient in amount to de-ionize the metal ion content of the water.

14. A wire drawing lubricant solution for beryllium-copper alloys, said solution consisting of an aqueous solution of the di-sodium monocadmium salt of ethylene diamine tetraacetic acid and alkali metal fatty acid soap, the amount of said soap being from 1% to 20% the amount of said di-sodium mono-cadmium salt and the amount of said di-sodium mono-cadmium salt being sufiicient with the water content of the solution to provide the desired density to the lubricant solution.

15. The wire drawing solution of claim '14, said solution containing about v25 grams of the said di-sodium mono-cadmium salt and about 2.5 grams of sodium stearate, and 2 to 5 grams of the tetra sodium salt of ethylene diamine tetraacetic acid per 1000 cc. of solution.

FREDERICK C. BERSWORTH.

REFERENGES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,008,939 Tufts July 23, 1935 2,320,392 White June 1, 1943 2,329,731 Spring Sept. 21, 1943 2,412,943 Bersworth Dec. 24, 1946 

14. A WITE DRAWING LUBRICANT SOLUTION FOR BERYLLIUM-COPPER ALLOYS, SAID SOLUTION CONSISTING OF AN AQUEOUS SOLUTION OF THE DI-SODIUM MONOCADMIUM SALT OF ETHYLENE DIAMINE TETRAACETIC ACID AND ALKALI METAL FATTY ACID SOAP, THE AMOUNT OF SAID SOAP BEING FROM 1% TO 20% THE AMOUNT OF SAID DI-SODIUM MONO-CADMIUM SALT AND THE AMONT OF SAID DI-SODIUM MONO-CADMIUM SALT BEING SUFFICIENT WITH THE WATER CONTENT OF THE SOLUTION TO PROVIDE THE DESIRED DENSITY TO THE LUBRICANT SOLUTION. 